Taylor-Dunn B0-248-TT, Operation, T Roubleshooting And Replacement Parts Manual, Page: 122 / 204

Maintenance, Service, and Repair
Electrical Troubleshooting
Page 12
Contactor Negative Return
The forward and reverse contactors coils use a common negative return that is provided by the
controller from Pin #3. The negative output from Pin #3 is part of a fault monitoring circuit in the
controller. If the controllers senses a short circuit in the controller output, it will not provide a negative
signal to the contactor buss preventing the contactor from closing.
Disconnect the Green power cable from the controller M- terminal.
Connect a test light from the controller M- terminal to the B+ terminal.
Connect a test light from the contactor negative buss to the B+ terminal on the controller.
NOTE: MUST USE TWO TEST LIGHTS!
Close the seat interlock switch and turn the key switch ON.
> The test light connected to the contactor negative buss should be ON.
> If the control system is working, the test light connected to the M- terminal should
vary in intensity depending on the position of the throttle pedal.
Negative buss test light is ON: Controller fault circuit working.
Negative buss test light is OFF: Perform tests at Controller Small Signal Input. If all good
then replace the controller.
Repeat the test with the Green wire reconnected to the M- terminal.
> If the test fails with the wire connected but passed with the wire disconnected,
then there is a short in the vehicle power wiring or motor.
These test procedures must be
performed in the order they were
written. If the test result is good,
then proceed to the next test or go
to the next section. Failure to do so
may result in incorrect test results.